Technical Field
The present disclosure relates to an electronic device for implementing digital functions and miniaturized logic gates, based on molecular functional elements, and to a method for digital computation implemented by such a device.
An electronic processing system, employing one or more of the above-mentioned devices, and a method for manufacturing the same device are also within the disclosure.
Description of the Related Art
The evolution of microelectronics, particularly applied to processors and electronic computers based on integrated circuits, has developed over the last decades while keeping the extraordinary pace foreseen by the so-called “Moore's Law”. This emerged particularly in the increasingly improved miniaturization of integrated electronic circuits, or in the increasing computational capacity that can be obtained while keeping dimensions constant, which in turn depends on the number of functional elements (for example, logic gates) that can be integrated in a given space, and on the operating speed of such functional elements.
This evolution was made possible due to improvements mainly in technology, while the founding principles of the micro-electronic circuits, which for decades have been based on transistors as base elements, remained unaltered.
Actually, the above-mentioned evolution involved the design, manufacturing and integration of more and more fast, miniaturized, and increasingly energy-efficient transistors. Regarding miniaturization, the key aspect was, and still is, the ability to use lithographic manufacturing processes on smaller and smaller spatial scales.
However, such technological evolution seems to be reaching its limit. Costs and feasibility of lithographic processes on scales that are smaller than the current ones appear to be problematic.
In order to overcome the barriers and limits set forth above, it is felt a need for a quality breakthrough related to concept itself of devices, processing systems, and electronic computers, according to what may be briefly defined as a transition from micro- to nano-electronics.
A transition from micro- to nano-electronics involves particularly applying physical laws that are even more fundamental than those employed in transistors, for example, quantum phenomena on an atomic-molecular scale.
Therefore, research in this field pursues the chance to devise so-called nano-electronic “transistor-like” devices (such as “molecular transistors” or “tri-gate transistors”) that, while being based on quantum phenomena, aim to reproduce the operation of conventional transistors. However, nano-electronic “transistor-like” solutions have severe drawbacks, since to date they do not allow obtaining the same performance of the state-of-the-art micro-electronic transistors. Furthermore, a transistor-based system includes complex interconnections, which are obtained by lithographic processes, thus not allowing overcoming the above-mentioned limitations of such lithographic processes.
A further line of research, mostly developed by academic institutions, relates to a type of so-called “transistor-less” devices, i.e., devices not involving the use of transistors.
This line of research comprises, e.g., QCAs—“Quantum-dot Cellular Automata”. QCAs are based on the principle that, since the properties of materials change radically at the nano-scale, at such a scale processing methods, exploiting quantum phenomena at an atomic-molecular scale, such as the electrostatic interaction combined with quantum tunneling effect and quantum charge confinement, can operate. Such processing methods can be much more efficient compared to those based on switches, such as transistors.
QCAs provide for functional units composed of, e.g., 6-dot cells (i.e., six atoms or groups of atoms), capable to assume two different polarized states and a neutral state, corresponding to different charge configurations around the different atoms or groups of atoms, each equivalent to a respective “confinement site”. Each cell can be obtained, for example, by means of two molecules, each of which comprising three confinement sites. The possibility to obtain, by means of QCAs, single functional units such as memory cells, binary lines, logic inverters, up to single Boolean logic gates, has been shown.
However, to date, QCAs did not prove to be capable of implementing complex processors, since the implementation of prior art complex QCA cell processors use substantially conventional lithographic processes, to the extent of the spatial resolution of a single QCA cell, with all the above-mentioned limitations thereof.
A further drawback of prior art QCA solutions, particularly at a molecular scale, is that they are implemented on the basis of molecules that are highly symmetrical in structure and electric configuration, while real molecules tend to be asymmetric, at least due to the deposition thereof on substrates, together with other possibly similar molecules.
The use of not exactly symmetric molecules is a severe limitation on the performance that can be obtained by QCAs.
From what has been stated above, it shall be apparent that the desire to provide nano-electronic integrated devices with digital processing performance comparable to those of current micro-electronic circuits and processors, and at a reasonable cost, is largely unmet.